Jökull - 01.12.1969, Blaðsíða 57

Sea Ice Drift in the East-Greeniand Current
THORBJORN KARLSSON,
SCIENCE INSTITUTE, UNIVERSITY OF ICELAND, REYKJAVÍK, ICELAND
abstract
A theory is presented describing the drift of
sea ice and Ihe changes in ice concentration.
The movernent of the ice is considered to be
affected by five different forces: xvind stress,
xvater stress, Coriolis force, pressure gradient
force due to a sloping sea surface, and internal
ice stress. The wind and water slresses are ob-
tained from Prandtl’s boundary layer theory.
The internal ice slresses are obtained by assum-
>ng the ice to be an isotropic, elastic medium.
The equation for ice concentralion is essen-
tially an equation of continuity for the float-
ing ice mass. The equation allows for creation
of new ice by freezing and disappearance of
ice by melting.
A solution of the equations wilh special re-
ference to the area of the East-Greenland Cur-
rent north of Iceland is discussecl briefly.
introduction
It is generally believed that most of the drift-
tng sea ice, which so often in the past has
covered the sea surface north of Iceland and
closed all navigation lanes in the area has been
brought down from the Arctic by the East-
Greenland Current. This current transports
most of the ice which flows out of the Arctic
and under “normal” conditions the ice stream
follows the east coast of Greenland and moves
southwestward through the Denmark Strait be-
tween Iceland and Greenland without stopping
111 Iceland. Normal conditions refer to the
climate as experienced over the past few de-
cades, by the majority of the present genera-
tion in Iceland, i.e. the years from 1920 until
after 1960. Many conditions can lead to the un-
scheduled visit of the ice to Iceland of which
the following can be listed (Karlsson 1969:)
1- Unusuallv heavy concentration of ice along
the coast of Greenland to the north of Ice-
land. The East-Greenland Current may not
be strong enough to carry all the ice south-
ancl southwestward, with the result that the
flow of ice widens and spreads out over a
large area. It is likely that under these
circumstances some ice may be pushetl out
of the East-Greenland Current into other
currents which subsequently carry it to Ice-
land.
2. Northerly and northwesterly winds of long
duration may carry some of the ice mass
out of the main ice stream along the east
coast of Greenland and towards Iceland.
3. Unusually light flow of water in the East-
Greenland Current or continuous south-
westerly winds may result in conditions
similar to those described under (1), even
though only normal flow of ice has been
carried from the north.
The first attempts to relate the drift of sea
ice to surface winds were made late in the last
century. The discovery of parts of the wreck-
age of the research vessel “Jeanette” on the
southwest coast of Greenland several years after
the ship was lost in the neighbourhood of the
New Siberian Islands in the Arctic in 1881,
gave the Norwegian explorer Nansen the iclea
to let his ship “Fram” drift with the ice. His
trip lastecl frorn September 29, 1893 until Au-
gust 17, 1896 and took him from the New
Siberian Islands to the area north of Spitz-
bergen. Nansen wrote a report on his observa-
tions (Nansen 1902) and Ekrnan based his well
known theory on wind currents (Ekman 1905)
on results obtainecl in the “Fram” expedition.
Several expeditions were made in the Arctic
in the years between the two world wars, and
many scientists made attempts to explain the
disagreement between Ekman’s theory and ob-
served wincl drift ot' ice. Among those were
Sverdrup (1928), Hidaka (1930) and Rossby and
Montgomery (1935). A vigorous research pro-
JÖKULL 19. ÁR 53